P5 - Newtons First And Second Laws

Question 1

What is newtons first law?

Answer 1

A resultant force is needed to make something start moving,speed up or slow down

Question 2

If the resultant force on a STATIONARY object is zero,what will the object remain as?

Answer 2

Stationary

Question 3

If the resultant force on a moving object is zero,what does it remain as?

Answer 3

It will carry on moving at the same velocity (same speed and direction)

Question 4

What does it mean if anything is moving at a constant velocity?

Answer 4

The resistive and driving forces on it all are balanced

Question 5

How does a velocity no stay constant?

Answer 5

If there is a non-zero resultant force acting on the object

Question 6

What does a non-zero resultant force always produce?

Answer 6

Acceleration or deceleration in the direction of the force

(This “acceleration” can take 5 different forms: starting,stopping,speeding up,slowing down and changing direction)

(On a free body diagram,the arrows will ALWAYS be unequal for non-zero resultant forces)

Question 7

What is newtons second law?

Answer 7

Acceleration happens when force happens on an object

(This means that acceleration is proportional to the resultant force)

Question 8

What does it mean if the resultant force gets larger?

Answer 8

The more the object will accelerate - the force and acceleration are directly proportional.You can write this as F ∝ a

Question 9

What is acceleration inversely proportional to?

Answer 9

The mass of an object - so an object with a larger mass will accelerate less than the one with a smaller mass (for a fixed resultant force)

Question 10

How do you calculate the resultant force?

Answer 10

Resultant force (N) = Mass (kg) x Acceleration (m/s2)

(This can be abbreviated to F = ma)

Question 11

A van of mass of 2080kg has an engine that provides a driving force of 5200N.At 70mph the drag force acting on the van is 5148N.Find its acceleration at 70mph

Answer 11

Resultant force = 5200 - 5148 = 52

F = ma

a = F / m = 52 / 2080 = 0.025 m/s2

Question 12

Estimate the resultant force on a car as it accelerates from rest to a typical speed

Answer 12

A typical speed of a car is ~25 m/s.It takes ~10s to reach this.

A = v / t = 25 / 10 = 2.5 m/s2

The mass of a car is ~1000kg

So using F = ma = 1000 x 2.5 = 2500 N

So the resultant force is ~2500 N